This invention relates to two part electrical connectors and in particular to those having removable filter contacts.
Standard non-filter contacts are conventionally held in place in such connectors by means of a plastic retention disc. The retention disc has an aperture for each contact and on one side of the disc are formed a number of resilient tines about each aperture projecting from the surface of the disc and angled inwards. The contact is pushed through the aperture from the other side (the rear) of the plate, the tines flexing to allow its passage and then engaging behind a flange or shoulder on the contact to prevent withdrawal. Removal is achieved by insertion of a tool from the rear of the plate to spread the tines so that they are clear of the shoulder and the contact can be withdrawn.
Known types of filter contacts give rise to problems when used with a retention disc of the type described. Filter contacts of the stress-isolated type, which are designed to allow a certain amount of bending of the metal part of the contact whilst having a fragile ceramic capacitive casing around a part of the contact, have conductive rubber washers or spacers compressed between the metallic ends of the contact, or flanges spaced along its length, and the ends of the ceramic capacitive casing in the centre. The spacers provide the necessary electrically conductive path whilst permitting a significant bending of the ends of the contact without putting stress on or causing damage to the fragile ceramic casing. Due to the spacers being held in compression, it is inevitable that the outer wall of each spacer will bulge outwards between the flange on the contact and the end of the ceramic casing. If a contact of this type is withdrawn through the retention disc described above, the free ends of the tines are prone to catch on the bulging outer wall of the spacers or the ends of the ceramic capacitive casing. Repeated insertion and withdrawal of such a contact can lead to damage of the spacers, ceramic casing and tines.
A further problem which is encountered in the design of such electrical connectors, particularly of those having a high contact density, is the provision of a ground plane. It is a fundamental requirement of a filtered connector that each of the individual filter contacts must have their capacitive elements connected to a common system ground point, usually via the connector casing. This is conventionally achieved by either soldering each contact to a conductive plate or by provision of a metallic plate having spring characteristic through which each contact passes and in which contacting tines are formed. Soldering prevents the removal of contacts and the close proximity of the contacts in high density connectors makes the formation of springy tines in metallic plate impracticable.
United Kingdom Patent GB 1,257,418 describes a plate having spring characteristics. The plate of GB 1,257,418 provides a number of separate electrical connections between a wiring board and a demountable component assembly. There is no suggestion of passing capacitive filter through apertures in the plate nor of connecting all the connection points together and to ground potential. United Kingdom Patent GB 950,047 describes an edge connector for printed circuit boards which uses a number of separate sprung metal contacts. As with GB 1,257,418, there is no suggestion of use with capactive filter contacts nor of electrically connecting all of the contacts together and to ground potential.